This invention relates to a method and apparatus for manufacturing metal sections, and more particularly to a method and apparatus for forming starting material with a quadrangular cross-section into a metal section with the desired cross-sectional shape.
Conventionally, blanks or semi-finished materials for the rolling of sections have been manufactured mostly by the primary-mill process, with some being manufactured by the continuous-casting process.
Outdone in efficiency, yield, energy consumption and some other respects, all the same, the primary-mill process is being increasingly supplanted, especially in Japan, by the continuous-casting process that casts molten metal continuously into blanks (or semi-finished sections).
But continuous casting itself is not without problems. The need of changing molds for different shapes and sizes lowers equipment utilization and production rates. Continuously cast intricate sections are subject to such quality problems as cracking and segregation during cooling. To insure high-quality, high-efficiency continuous casting, the cross-sectional shape of the casting must be as close as possible to a flat rectangular shape. Another important requisite is that the size of the casting vary as little as possible, or the quantity of each size lot be as large as possible. Such quadrangular casting is then formed into blanks of various shapes and sizes by a subsequent process.
Primary mills for rolling quadrangular materials into blanks, especially those comprising paired horizontal rolls with shape passes, require that the starting material have a large enough cross-sectional area to secure the desired flange width. This unavoidably entails an increase in threading frequency and a drop in productivity.
Use of universal mills for the rolling of quadrangular materials into blanks has also been proposed, with a promise of much lower threading frequency than with the grooved rolls. In rolling, on whatever type of mill, however, metal flow in the rolling direction is inevitable, which is made up for by the supply from the flange portion. The result is a metal shortage in the flange portion and a failure to secure the desired flange width. Universal mills are no exception.